i386 with 4GB RAM: less than 2GB available on A2SAV (Intel Atom E3940)

[Andre Albsmeier]

On Sun, 28-Jan-2018 at 10:32:44 -0600, Mike Karels wrote:
> > On 28 Jan 2018, at 15:57, Andre Albsmeier <Andre.Albsmeier at siemens.com> =
> > wrote:
> > > I have a lot of machines running with 4 GB physical RAM and, for
> > > some reasons, I still have to use a 32 bits OS.
> > >=20
> > > All of them show something between 3 and 3.5 GB of RAM available
> > > in dmesg but the brand new Supermicro A2SAV really shocked me:
> > >=20
> > > FreeBSD 11.1-STABLE #0: Mon Jan 15 06:57:10 CET 2018
> > > ...
> > > real memory  =3D 4294967296 (4096 MB)
> > > avail memory =3D 1939558400 (1849 MB)
> > > ...
> > >=20
> > > So do people have any ideas how I might get a bit closer to at least
> > > 3 GB? I assume there are no FreeBSD knobs which might help but hope
> > > dies last...
> 
> > This is a common problem on i386.  Most likely some ranges are reserved
> > for I/O mappings, such as video cards.  If you boot with -v, I think the
> > kernel prints an overview of the physical ram chunks available?  I don't
> > know of any other way to get such an overview.
> 
> > Another option is to try PAE, but I have no idea how stable that is...
> 
> > -Dimitry
> 
> I suspect that the unavailable RAM has been mapped above 4 GB by the BIOS.
> 
> About PAE: at $JOB, we have a FreeBSD 8.2 system that has been running
> PAE reliably since 8.2 was new.  Also, we ship amd64 systems that run
> mostly 32-bit binaries, which works well.

Finally I found some time to play with the PAE option. I added

option     PAE
option     KVA_PAGES=1024

and the A2SAV booted and gave me

real memory  = 4294967296 (4096 MB)
avail memory = 4048207872 (3860 MB)

Very encouraging, this is double of what I had before! So I decided to try
this on my desktop machine which also boots but loading the i915kms and drm2
stuff fails with

info: [drm] Initialized drm 1.1.0 20060810
drmn0: <Intel IvyBridge> on vgapci0
error: [drm:pid949:i915_gem_gtt_init] *ERROR* Scratch setup failed
device_attach: drmn0 attach returned 12

The KMS stuff doesn't support the A2SAV anyway so I can't test how
it would behave there...